(1) Field of the Invention
The present invention relates to a drill mainly used for drilling of carbon fiber reinforced plastic (CFRP) and the like.
(2) Description of Related Art
When drilling of components (members) used for automobiles, aircrafts and the like is performed, various drills are used depending on materials of the components. If a work material is made of metal such as aluminum, the drill is required to have ability not to adhere to the work material in order to prevent clogging of swarf. Further, if the work material is a high-density fiber material such as CFRP, the drill is required to have ability to suppress occurrence of inter-layer peeling and a burr due to a fiber material in order to secure accuracy of the drilled hole.
For example, Japanese Patent No. 4120319 discloses that a flank of a drill is configured by a first flank including a cutting edge, a second flank formed on a rear side of the first flank in a rotational direction, a third flank including a chisel edge, and a fourth flank consisting of a step surface formed between the second flank and the third flank, and the fourth flank increases toward an outer peripheral direction, so that adhesion of a work material and the drill due to cutting heat is prevented when the work material is made of an alloy of aluminum or the like. FIG. 4 shows an enlarged perspective view of a tip end portion of the drill.